The improvements of this invention relate to natural gas engines, particularly to single-cylinder natural gas engine with a four-stroke cycle. It relates generally to the fuel supply system disclosed in U.S. Pat. No. 4,886,034, which discloses a four-stroke cycle, single-cylinder engine for a residential heat pump wherein the fuel supply manifold communicates with a venturi carburetor having a venturi element and an air bypass passage, the latter being controlled by a throttle valve that is distinct from the speed control throttle valve located in a fuel supply manifold on the downstream side of both the venturi element and the bypass passage. The throttle valve and the bypass passage of the device of the '034 patent compensate for normal tendencies of the air/fuel ratio to vary in magnitude as the engine speed changes. They may be used also as an enrichment mechanism to facilitate engine starting.
Fuel is supplied to the throat of the carburetor of the '034 patent by a means of a supply passage defined in part by a gas pressure governor that includes a diaphragm valve having a diaphragm that is actuated in response to the pressure differential between the throat of the carburetor venturi and the pressure at the air intake of the carburetor. An attempt is made in the control of the '034 patent to maintain a high operating efficiency for the engine by using a pre-programmed microprocessor that responds to sensed engine speed and manifold pressure changes to control the throttle valve and the bypass passage around the carburetor venturi. Pressure pulsations that are due to the opening and the closing of the intake valve for the single cylinder can be offset by appropriately calibrating the microprocessor to compensate for the pulsating pressure of the air that flows through the carburetor throat. Compensating adjustments in the bypass throttle valve are made in response to output signals developed by the microprocessor as the microprocessor responds to the instantaneous data that is measured by the manifold pressure sensor and the engine speed sensor.
Gas governor valves for gas engines are used in other environments such as the auxiliary gas valve system for a diesel engine described in U.S. Pat. No. 3,540,419. The engine described in the '419 patent is a diesel engine that is capable of using gaseous fuel under heavy load conditions, the gaseous fuel being supplied through a fuel flow control system from a liquid petroleum supply tank. The pressure of the gas fuel supplied to the engine intake manifold is regulated by a diaphragm valve that responds to the difference in the pressure of the air on the downstream side of the air filter and the pressure on the gas supply side of a diaphragm actuator for the gas valve. The opposite side of the diaphragm is exposed to the pressure on the downstream side of the air filter. Communication between the downstream side of the air filter and the air side of the diaphragm is established by an orifice valve and by a calibrated flow control orifice, the orifice valve in turn being sensitive to a thermal switch that senses engine load. A shut-off valve is located between the gas supply and the gas valve so that the gas supply may be interrupted when the engine operates in the normal fashion with its liquid diesel fuel injectors.
Attempts have been made in prior art designs to operate single-cylinder engines having a venturi carburetor so that a nearly constant air/fuel ratio is achieved over wide operating ranges of speeds and loads. It has been found, however, that a constant air/fuel ratio cannot readily be obtained because of the unsteady intake air flow associated with single-cylinder operation. This problem is aggravated if an air intake silencer is used because the silencer generates additional pressure pulsations at its natural frequencies. It has been found that the natural frequencies due to the silencer at certain engine speeds may become resonant with respect to engine cyclic frequency.
A typical fuel system having a traditional venturi carburetor may have a solenoid-operated enrichment device to assist cold starting.